Electromagnetic actuating device



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ELECTROMAGNETIC ACTUATING DEVICE Filed March 22, 1968 v 5 Sheets-Sheet 5 JAMES C. MACY A TTORNE Y5 United States Patent 3,467,927 ELECTROMAGNETIC ACTUATING DEVICE James C. Macy, Lavallette, N.J., assignor to Thrust, Incorporated, New York, N.Y., a corporation of New York Continuation-impart of applications Ser. No. 486,454, Sept. 10, 1965, and Ser. No. 663,792, Aug. 28, 1967. This application Mar. 22, 1968, Ser. No.

Int. Cl. H011? 7/13 US. Cl. 335-296 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electromagnetic actuating devices and, more particularly, to a novel type of electromagnetic actuating device capable of providing a powerful mechanical force over a relatively long traverse. This application is a continuation-in-part of applications Ser. No. 486,454, filed Sept. 10, 1965 (now Patent No. 3,376,- 528, issued Apr. 2, 1968) and Ser. No. 663,792, filed Aug. 28, 1967.

The conventional electromagnetic relay includes an electrical coil, a movable magnetic armature, and a magnetic structure for completing the flux path around the coil. Devices of this general structure can provide a relatively powerful mechanical force as the armature is attracted in response to energization of the coil. However, the magnitude of the force is inversely proportional to the square of the working air gap length associated with the armature. Thus, any attempt at increasing the length of the stroke brings about a decrease in the force at the beginning of the stroke which is approximately proportional to the square of the distance to be traversed. Electrical devices of this general structure are, therefore, inherently short stroke devices.

By comparison, the conventional plunger-type solenoid is inherently a long stroke device and usually includes an iron plunger adapted to pass through the center of an electromagnetic coil. The mechanical force is created by the interaction between the magnetic flux of the plunger and the current passing through the energizing coil. The force created by the solenoid is relatively weak and suffers from the further disadvantage of being strongest at the middle of the stroke and weakest at the ends where maximum force is often required.

Electromagnetic devices can be classified either with the inherently short powerful stroke devices, or with the relatively long weak stroke devices. Because of the inherent characteristics of the prior electromagnetic devices, it has not been possible to achieve a powerful force over a relatively long traverse without resorting to various boosting or supplementing techniques.

A principal object of this invention is to provide a technique for substantially increasing the pull which can be achieved by electromagnetic structures.

An object of this invention is to provide an electromagnetic actuator capable of converting electrical energy into a relatively powerful force over a long traverse.

Another object of the invention is to provide an electromagnetic actuator which can achieve optimum performance for given size, weight, geometrical configuration and electrical powerconditions.

Another object is to provide an electromagnetic actu- 3,467,927 Patented Sept. 16, 1969 ator in which the created force can be controlled as desired throughout the stroke.

Still another object is to provide an electromagnetic actuator which can be readily mass produced and in which standardized components can be assembled to satisfy varying operational requirements.

Yet another object is to provide an electromagnetic device which can easily be integrated as an operational portion of a system.

According to the technique developed according to this invention, a magnetic fluid or elastic medium such as oil or cellular rubber containing iron particles, is used to fill the air gap of the magnetic device. The magnetic fluid vor medium has been found to substantially increase the magnetic pull provided by the device.

Although not limited thereto, this technique is particu larly useful in electromagnetic devices which convert electrical energy directly into mechanical force and which are capable of providing a powerful mechanical force without limitation on the length of the stroke or traverse. The force is created by the magnetic attraction exerted upon a plurality of interconnected magnetic members. The working gap is filled with a magnetic fluid and broken into small increments so that a substantial force can be created without suffering the normal effects associated with a long stroke.

The invention is described in greater detail with reference to the following specification which sets forth several illustrative embodiments. The drawings are part of the specification wherein:

FIGURE 1 is a view of the actuating device filled with a magnetic fluid with portions of the structure broken away for clarity of illustration;

FIGURE 2 is an exploded perspective, assembly drawing showing details of some of the components for the actuating device in FIGURE 1;

FIGURES 3A and 3B are schematic diagrams illustrating two arrangements for interconnection of the electromagnetic coils for the unit in FIGURE 1;

FIGURE 4 is a partial cross-sectional view illustrating another embodiment of the invention; and

FIGURE 5 is a cross-sectional view of another actuating device wherein a single energizing coil is employed and the working gaps are filled with a solid elastic medium.

The mechanical force created by an electromechanical device can be expressed by the following formula:

F uA

where P is the pull or force, k is a constant, F is the magnetomotive force, ,u is the permeability of the working gap, A is the area of the pole face, and x is the length of the working gap. It should be noted that the created force is inversely proportional to the length of the working gap. In addition, the magnetomotive force is inversely related to the gap length and therefore the force falls oil rapidly as the working gap length increases.

In the illustrative embodiments, structures are described which provide a powerful force over a relatively long traverse which would normally require a corresponding long working gap. With the structure in accordance with the invention, the working gap is broken into relatively small increments to eliminate the problems associated with the long working gap. The structure also makes possible a relatively high magnetomotive force by minimizing the flux losses and by permitting use of materials in the working gap having a permeability greater than air.

The actuating device in accordance with one embodiment of the invention is illustrated in FIGURES l and 2, and includes a plurality of disc-shaped members 10, for convenience referred to as coil discs, each including an inner ring 11 and an outer ring 12. A concentrically wound electrical coil 14 is located between the inner and outer rings of the disc which form core pieces for the coil. A shoulder is machined in the upper and lower edges of rings 11 and 12 for positioning a pair of non-magnetic washers 15 above and below coil 14. Coil 14 can therefore be completely enclosed to avoid exposure to the surrounding fluid.

Inner core piece 11 includes a groove 16 extending from its inner surface to thereby provide an upper annular flange 17 and a lower annular flange 18. As associated coupling disc 20 is externally machined about its periphery to cooperate with the groove and flanges on the inner surface of core piece 11. The thickness of the coupling disc is the same as the thickness of coil disc 10. A circumferential groove 21 is machined surrounding disc 20 to provide upper and lower peripheral flanges 22 and 23. The coupling discs 20 are loosely mounted on a guide shaft 26 passing through the center thereof with a coupling disc located between each adjacent pairof coil discs. The flanges on the inner core pieces of adjacent coil discs rest within the groove 21 of the associated coupling disc and the flanges of adjacent coupling discs rest within the groove 16 of the associated inner core piece. This interlocked groove and flange arrangement permits the coil discs to move together until they touch one another, or to separate until the flanges engage. Thus, the coupling discs limit the separation between coil discs and hence, determine the maximum working gap which can exist between adjacent coils and core pieces. Guide shaft 26 maintains the coil discs in alignment parallel to one another and insures that the movement of the coil discs is linear and parallel to the axis of the shaft.

The end gap 30 is preferably machined from a single piece of iron and includes an annular recess dimensioned to accommodate a circumferentially wound electrical coil 31 and a nonmagnetic washer 32. A coupling member 34 is pivotably mounted in the center of end cap 30 in a manner which prevents any longitudinal movement relative to the end cap. The coupling member is constructed so that the portion extended above the end cap (as viewed in FIGURE 2) is essentially the same as the portion of a coupling disc extending from one of the coil discs. More specifically, coupling member 34 includes a peripheral flange 35 adapted to rest within the groove 16 of the adjacent coil disc, and a groove 36 adapted to cooperate with the flange of the adjacent coil disc. The other end of the coupling member is shaped as required for attachment to external equipment.

The upper and lower end caps for the actuating device are essentially the same and are attached to the upper and lower coil discs in the same fashion as is illustrated in FIGURE 1. The coupling members 34 each include a central recess 37 therein adapted to loosely hold guide rod 26. The length of the guide rod and the length of the cooperating recesses are selected so that the rod cannot fall out when the actuating device is in the fully extended condition but at the same time permit the actuating device to contract until the coil discs touch one another.

Although the flanges 22 and 23 on the coupling disc and flanges 17 and 18 in the coil disc are shown as complete circumferential flanges, they could be formed as flange segments covering somewhat less than half of the circumference. Such an arrangement would have assembly advantages, since the coupling disc could then be in serted within a coil disc and thereafter turned so that the flange segments become juxtaposed.

A flexible bellows-like cover structure 40 is mounted surrounding the unit to prevent fluid inside the structure from escaping. The outer rings of the coil discs are provided with grooves 41. Retaining rings 42 surround the bellows cover structure and cooperate with grooves 41 to maintain the cover in its proper position.

Retaining rings 42, coupling discs 20, coupling members 34 and guide rod 26 are preferably constructed from 4 nonmagnetic materials such as aluminum or brass. The inner and outer core pieces 11 and 12, and the end caps 30, are constructed from a magnetic material such as iron and can be laminated if desired to reduce eddy current losses.

The electrical leads from the coils 14 and 31 can be brought out through suitable holes in the outer core pieces and end caps. If the coils are interconnected so that current flows through each coil in the same direction, for example, the clockwise direction as shown in FIGURE 3A, the coil discs will be attracted to one another and an overall contracting force is provided as indicated by the arrows. On the other hand, if the coils are interconnected in an alternate fashion as shown in FIGURE 3B where current passes through one coil in a clockwise direction and through adjacent coils in a counterclockwise direction, the coil discs tend to repel one another and an overall expanding force is provided as indicated by the arrows. With suitable external switching, the same unit can be used to provide either a contracting or expanding force. The electrical coils can be energized simultaneously or sequentially depending on the type of motion desired.

The maximum linear traverse of the actuating unit, that is, the maximum distance that one end coupling member moves relative to the other when the coils are energized, is equal to the sum of the incremental working gaps 45 existing in the fully extended condition. If it is desired to increase the travel distance, this is easily accomplished by adding additional coil discs and coupling discs intermediate end caps 30. Therefore, the travel disance can be increased without decreasing the created force, since the force is a function of the working magnetic gap associated with the individual coils. This working gap in turn is limited by the coupling discs so that a working magnetic contact is maintained between the core pieces of adjacent coil discs.

The working gaps 45 are filled with a fluid medium having a permeability substantially greater than air. A convenient fluid medium is oil carrying iron particles. The oil also provides damping and heat dissipation as beneficial side effects in addition to reducing flux losses and decreasing the reluctance of the magnetic path.

Another embodiment of the invention is illustrated in FIGURE 4 wherein the inner rings or inner core pieces 11 of the coil discs are loosely mounted directly upon guide rod 26. The maximum gap 47 between adjacent coil discs is limited by inwardly flanged nonmagnetic coupling rings 46 which surround the adjacent flanges 48 of the adjacent coil discs. The coupling rings thus replace the coupling discs as well as the surrounding dust cover shown in FIGURE 1. The gaps 47 are filled with a magnetic fluid medium.

Another embodiment of the invention, utilizing a single electrical coil, is shown in FIGURE 5. The coil 50 is a cylindrical, concentrically wound, coil encased in a suitable nonmagnetic material providing relatively smooth exterior surfaces. One end of coil 50 is accommodated within a suitably dimensioned resistively coated annular recess 51 in an end cap 52. In recess 51, between the end of coil 50 and the bottom of the recess, is "a fiat coil spring 53 constructed from an electrically conductive material. The coil spring maintains electrical contact between an external lead 54 and one of the electrical leads 55 emerging from coil 50. The other end of coil 50 is similarly accommodated in an annular recess 61 within an end cap 62. The other lead 65 of coil 50 is coupled to an external lead 64 via a coil spring 63 located within recess 61. End caps 52 and 62 include extensions 57 and 67, respectively, adapted for attachment to external equipment.

Within the central opening of coil 50 there is a plurality of internally grooved and flanged discs 76 which are coupled to one another and to the end caps by means of externally grooved and flanged coupling discs 77. The coupling discs serve to limit the length of the working gap in essentially the same manner as previously described with respect to FIGURES 1 and 2. A plurality of externally flanged and grooved discs 78 surrounds coil 50 and are coupled to one another and to the end caps by means of internally flanged coupling rings 79, The coupling rings operate to limit the length of the air gap between discs 78 in essentially the same manner as previously described with respect to FIGURE 4.

End caps 52 and 62, and discs 76 and 78, are prefera-bly constructed from a magnetic material such as iron, whereas coupling discs 77 and coupling rings 79 are preferably constructed from a nonmagnetic material.

The working gaps 80 are filled with a highly elastic magnetic medium such as sponge rubber or cellular rubber impregnated with iron particles. With this arrangement, it. is not possible to completely close the working gaps, but the high degree of compressibility of the sponge and cellular rubbers nevertheless permit asubstantial movement of the discs 76 and 78. This arrangementeliminates the need for fluid seals and better confines the magnetic path to eliminate stray flux.

While only a few embodiments have been specifically illustrated, it should be obvious that the technique for increasing the magnetic pull of an electromagnetic actuating device has wide application in structures other than those specifically illustrated. For example, the force created by a conventional solenoid can be increased by filling the air gap with a magnetic fluid medium and by providing a suitable fluid-containing enclosure as another example.

I claim:

1. In a magnetic actuating device, the combination of a pair of end members capable of movement along a common axis;

a magnetic structure disposed'between said end members and including a plurality of magnetic segments surrounding said common axis for dividing any existing gap into a plurality of increments;

an elastic medium having ferromagnetic properties filling said incremental gaps formed by said magnetic structure; and

electromagnetic means operatively associated with said magnetic structure for creating a magnetic flux when energized, which magnetic flux passes through said magnetic segments and said elastic medium to cause relative movement of said end members along said common axis.

2. A magnetic actuating device according to claim 1 wherein said elastic medium is a fluid medium comprising oil with ferromagnetic particles therein.

3. A magnetic actuating device according to claim 1 wherein said elastic medium is a fiuid medium comprising a silicone fluid with ferromagnetic particles therein.

4. A magnetic actuating device according to claim 1 wherein said elastic medium is a highly expanded rubberlike material with ferromagnetic particles therein.

5. In a magnetic actuating device, the combination of a pair of relatively movable magnetic end members capable of movement along an axis for closing a working gap therebetween;

an elastic medium having ferromagnetic properties fill-,

ing said working gap formed between said end members; and

electromagnetic means operatively associated with said magnetic end members for creating a magnetic flux when energized, which magnetic flux passes through said magnetic end members and said elastic medium to cause relative movement of said end members along said axis to at least partially close said working gap.

6. A magnetic actuating device according to claim 5 wherein said elastic medium is a fluid medium comprising oil with ferromagnetic particles therein.

7. A magnetic actuating device according to claim 5 wherein said elastic medium is a fluid medium comprising a silicone fluid with ferromagnetic particles therein.

8. A magnetic actuating device according to claim 5 wherein said elastic medium is a highly expanded rubberlike material with ferromagnetic particles therein.

References Cited UNITED STATES PATENTS 548,601 10/1895 Black 335-259 XR' 1,699,866 1/1929 Werner 335264 2,792,536 5/1957 Immel 335279 2,881,367 4/1959 Watson 335-279 XR G. HARRIS, Primary Examiner. 

